The present invention relates to an embedded magnet type motor.
Conventionally, a rotor core of an embedded magnet type motor has a plurality of accommodation holes accommodating a plurality of magnets. A plurality of magnets are distributed in a circumferential direction of the rotor core. Each of the accommodation holes passes through the rotor core in an axial direction.
An embedded magnet type motor disclosed in Japanese Laid-Open Patent Publication No. 2005-51982 has plural pairs of magnets arranged so as to form a V shape. The V shape projects inward in a radial direction. Each pair of the magnets form one magnetic pole. In other words, in the case that the number of the magnetic poles of the embedded magnet type motor is represented by P, the number of magnets required in the whole of the motor is represented by 2P. In this case, for example, in comparison with a motor in which curved or linear magnets are arranged simply along a circumferential direction, a greater number of magnets can be used, and it is possible to achieve a high torque.
However, in the embedded magnet type motor having magnets, the number of which is represented by 2P, the number of parts is increased, and a parts management cost and an assembling cost may be increased.
The embedded magnet type motor in the publication mentioned above has a plurality of outer bridges defined between an outer end in a radial direction of each of the accommodation holes for accommodating the magnet, and an outer circumferential surface of the rotor core. Two outer bridges are provided in one magnetic pole. Accordingly, a leakage flux passing through the outer bridge is too much for the entire motor. As a result, an effective magnetic flux of the embedded magnet type motor is reduced, and a high torque cannot be obtained.